My 1995 Maxima with 80,000 miles has problems starting when it sits overnight, usually in cold weather. In the last two months, I've replaced the battery, starter, spark plugs, air filter and fuel filter and it still takes two or more tries to crank it before it starts. It sounds like something is draining the battery overnight. Any suggestions would be greatly appreciated.

Try this simple test
 

Does the engine crank (Rrr-Rrr-Rrr) at normal speed but fail to fire (Vroom)? Please try this simple experiment and report your results. When the engine is cold, turn the key to ON, wait 15 seconds, and then turn the key to START. If the engine starts readily after this brief delay, it could indicate a loss of residual fuel pressure. If the engine is still difficult to start, it could indicate a faulty Engine Coolant Temperature Sensor.

Re: Try this simple test
 

Daniel, this simple test seemed to work this morning (it was about 30 degrees). I waited 15 seconds with the key in the ON position and then turned the key to START and the engire started readily (Vroom). What can I do about a loss of residual fuel pressure? I've already replaced the fuel filter and had the fuel system and throttle body cleaned. Do I need to change the fuel to a higher octane level?

Presumed loss of residual fuel pressure
 

That's encouraging. Please continue to make this test for the next few days to see if the results are consistent.

When your engine is running the fuel rail pressure should stay in the 34 - 43 psi range. When your engine is switched off that pressure should be maintained. This is called residual pressure. The presumed loss of residual pressure can be confirmed by a fuel pressure test. This is done by installing a T-fitting in the rubber fuel line just downstream of the fuel filter. This is a standard diagnostic test. You will find it in Chilton (page 5-3) or Haynes (page 4-3).

If a loss of residual pressure is confirmed, it indicates a fuel leak. Fuel leaks are external or internal.

An external leak is one which allows the fuel to escape from the fuel system.
It might be caused by
- a leaky rubber fuel line which allows fuel to escape into the atmosphere
- a sticking fuel injector which allows fuel to escape into the intake manifold

An internal leak is one which allows the fuel to escape from the fuel rail back into the fuel tank.
It might be caused by
- a faulty fuel pump check valve
- a bad fuel pressure regulator

There are ways to identify the specific source of the leak but let's get into that only when you are certain that the problem is loss of residual pressure. In the meantime, drive with confidence. This is not a serious problem and you are not aggravating the problem by postponing the repair.

The fuel filter and throttle body will not affect residual pressure.

No. Octane level, more properly called Anti-Knock Index (AKI), is unrelated to this problem.